Contact bridge system for circuit breaker

ABSTRACT

A circuit breaker bridging contact is constructed as a U-shaped member having L-shaped arms to more efficiently utilize electrodynamic forces to achieve current limiting action. Upon circuit opening parallel arcs re drawn between the bridging contacts and the spaced stationary contacts. The currents flowing in these arcs are in directions opposite to current flowing in those portions of the bridging contact arms that are parallel to the arcs and relatively close thereto, so that electrodynamic forces tend to drive the arcs away from the separating contacts. Speed of contact separation is improved by having the web of the bridging contact in close proximity and parallel to a rigidly held conductor section through which current flows in a direction opposite to that of current flowing through the bridging contact web.

United States Patent Kussy et al.

[15] 3,663,905 1 1 May 16, 1972 [54] CONTACT BRIDGE SYSTEM F0 CIRCUIT BREAKER [72] Inventors: Frank W. Kussy, Haverford; Gustave E.

Heberlein, Jr., King of Prussia, both of Pa.

[73] Assignee: I-T-E Imperial Corporation, Philadelphia,

22 Filed: May 20,1971

21 Appl.No.: 145,176

[52] U.S.Cl ..335/l95 [51] lnt.Cl. ...H0lh 77/10 [58] Field ofSearch .335/195. 16

[56] References Cited UNITED STATES PATENTS 3,092,699 6/1963 Latour ..335/195 3,419,828 12/1968 Bremer 3,593,227 7/1971 Mitskevieh et al ..335/l95 Primary Examiner-Harold Broome [5 7] ABSTRACT A circuit breaker bridging contact is constructed as a U- shaped member having L-shaped arms to more efficiently util' ize electrodynamic forces to achieve current limiting action. Upon circuit opening parallel arcs re drawn between the bridging contacts and the spaced stationary contacts. The currents flowing in these arcs are in directions opposite to current flowing in those portions of the bridging contact arms that are parallel to the arcs and relatively close thereto, so that electrodynamic forces tend to drive the arcs away from the separating contacts. Speed of contact separation is improved by having the web of the bridging contact in close proximity and parallel to a rigidly held conductor section through which current flows in a direction opposite to that of current flowing through the bridging contact web.

1 1 Claims, 16 Drawing Figures PATENTEDMAY 16 I972 LOW FA UL 719 SHEET1UF4 THEE/W44 CURVE 5' more particularly relates to a current limiting circuit breaker.

utilizing a bridging-type movable contact of particular construction to achieve more efiicient utilization of electrodynamic forces to achieve rapid contact separation and are extinction.

The electrodynamic effect resulting from the interaction of electric fields which accompany current flow has been utilized to achieve so-called current limiting action in'circuit breakers by achieving a degree of contact separation before the circuit breaker operating mechanism is able to achieve contact separation. In prior art breakers of this type the electrodynamic force has been utilized principally to achieve contact separation. However, once contact separation is achieved, arc extinction is a major problem because of the high current involved.

In accordance with the instant invention, a double break is achieved by utilizing a bridging contact which is generally of U-shape and having arms that are generally L-shaped. The web of the U is parallel to and in close proximity with a rigidly held conductor that carries current in a direction opposite to current flowing in the contact web so that an electrodynamic repelling force acts between the rigidly held conductor and the movable contact. The L-shaped arms provide conducting portions that are close to the gaps between the separating contacts and have currents flowing opposite to the directions of the currents flowing in thearcs across the gap, so that these arcs are moved off of the contacts.

Accordingly, a primary object of the instant invention is to provide a novel construction for a current limiting circuit breaker which provides for efiective utilization of electrodynamic forces to achieve rapid contact separation and rapid arc extinction.

Another object is to provide a circuit breaker of this type which utilizes a bridging contact to obtain a double break.

A further object is to provide a circuit breaker of this type in which the bridging contact is generally of Ushape and has generally L-shaped arms.

These objects as well as other objects of this invention will become readily apparent after reading the following description of the accompanying drawings in which:

FIG. 1 is a graph showing a comparison between the tripping characteristics of a current limiting circuit breaker constructed in accordance with the instant invention and a current limiting circuit breaker of the prior art.

FIG. 2 is a side elevation of a molded case current limiting circuit breaker constructedinaccordance with teachings of the instant invention, with the near side of the housing removed to reveal the essential operating and current carrying elements.

FIG. 3 is a fragmentary portion of FIG. 2, illustrating contact opening due solely to action of the spring operating mechanism.

FIG. 4 is a fragmentary portion of FIG. 3, illustrating contact opening under conditions where the magnetic tripping device exerts a mechanical force to assist the spring operating mechanism.

FIG. 5 shows the elements of FIG. 4 when contact opening is due solely to mechanical forces developed by the magnetic tripping means.

FIG. 6 is a fragmentary portion of FIG. 3, illustrating contact opening under conditions where electrodynamic forces assist the mechanical force of the magnetic tripping means.

FIG. 7 shows the elements of FIG. 6 under conditions where contact separation is due solely to electrodynamic forces.

FIGS. 8 and 9 are perspectives of the movable stationary contacts looking at opposite sides thereof.

FIG. 10 is an end view of the contacts looking in the direction of arrows 10-10 of FIG. 8.

FIG. 11 is an end view of the contacts looking in the direction of arrows 11-11 of FIG. 9.

FIG. 12 is a view similar to that of FIG. 10 with the addition of insulating barrier elements.

FIG. 13 is a cross-section taken through line 13-13 of FIG. 12 looking in the direction of arrows 13-13.

FIG. 14 is an enlarged view of the operating magnet under normal load current conditions.

FIG. 15 is a side elevation of the magnet yoke and armature under fault current conditions.

FIG. 16 is a side elevation of the magnet armature looking in the direction of arrows 1616 of FIG. 15.

Now referring to'the figures. As illustrated by curve A in FIG. 1, the tripping characteristic of prior art molded case current limiting circuit breakers is generally divided into two regions C and D. In the first region C the magnetic trip device of the breaker releases a latch, permitting energy stored in the operating springs to open the contacts. In region C, fault currents are in the low to medium range, or typically from five to 50 times the maximum continuous current rating of the breaker, and very little current limitation takes place because contact opening speed is relatively slow.

In the second region D, the fault currents are higher than in region C,"and the circuit breaker contacts are opened independently of the circuit breaker operating mechanism. The major share of current limitation takes place in region D since the contacts are opened before current has reached the maximum available peak. At this time the contacts are opened at a speed that is high enough to draw and develop a high arc voltage which opposes the driving voltage of a system until current arrives at zero.

As will hereinafter be seen, circuit breaker or circuit interrupter 20 (FIG. 2), constructed in accordance with the instant invention, has a tripping characteristic illustrated by curve B. The differences between curves A and B are due to the fact that circuit breaker 20 achieves faster contact separation in the range of medium fault currents without adversely effecting tripping at low fault currents or very high fault currents.

Circuit breaker 20 of FIG. 2 is a multi-phase unit, only one phase of which is illustrated in the drawings. In particular, circuit breaker 20 includes molded insulating compartmented hollow base 21 having removable molded insulating cover 22 with opening 23 through which manual operating handle 24 extends. Handle 24 controls operation of a standard type overcenter spring operating mechanism 25 which operates automatically upon the occurrence of predetermined fault conditions. Mechanism 25 includes main operating tension spring 26 connected between handle 24 and knee 27 of the toggle formed by links 28, 29. Upper link 28 is pivotally connected at 31 to cradle 32. The latter is mounted at one end to pivot 33 and at its other end is provided with latch tip 34 engageable by latch 36 of a standard type automatic trip mechanism 35. The latter includes thermal tripping means (not shown) which provides delayed tripping under low fault conditions in the region over which curve portion E extends.

The lower end of lower toggle 29 is connected by pin 37 to the main contact arm portion 38 which is pivotally mounted on a center extending through insulating tie bar 41. Pivot pin 40 connects auxiliary movable contact arm 39 to the end of main arm 38 remote from tie bar 41. Bridging contact 42 (FIG. 8) is mounted to auxiliary arm 39 at the left end thereof and provides a part of the main current path through circuit breaker 20. This current path consists of line terminal 43, conducting strap 44, stationary contact 45, bridging contact 42, stationary contact 46, conductor 47, magnet coil 48, strap 49 including bimetal heater portion 50, and load terminal 51.

With reference to FIGS. 8-13, it is seen that the shape of contact means 42 is adapted to utilize electrodynamic forces for bringing about separation of bridging contact 42 from stationary contacts 45, 46 under severe fault conditions. In particular, bridging contact 42 is a modified U-shaped member including spaced parallel generally L-shaped arms 53, 54 joined by web or connecting section 52. The free ends of arms 53, 54 carry movable contacts 55, 56, respectively, which overlie and are engageable with stationary contacts 45, 46. Conductor 47 is connected at one end to conducting block 57 which supports stationary contact 46. The portion 470 of conductor 47 that extends parallel and adjacent to bridging contact connecting section 52 is rigidly held with respect to base 21.

Thus, currents I flow in opposite directions in conductors 52 and 47a so that magnetic fluxes accompanying such currents interact to produce an electrodynamic force indicated by double-headed arrows 61. Because conductor section 47a is rigidly held, this electrodynamic force moves bridging contact 42 upward with respect to FIG. 8, thereby separating movable contacts 55, 56 from stationary contacts 45, 46. As the separation takes place, electric current arcs 62 are formed. Magnetic flux generated by arcs 62 interact with the fluxes of currents flowing in the sections of arms 53, 54 generally parallel to are 62, with the result that an electrodynamic force is present, tending to elongate arcs 62 by driving them in the direction indicated by arrow 63.

As seen in FIGS. 12 and 13, insulating barrier plate 65 is positioned between stationary contacts 45, 46 and extends into notch 66 in the contact carrying end of molded insulating auxiliary arm 39'. Thus, with circuit breaker 20 open, the air path between stationary contacts 45 and 46 is a path having a narrow U-shaped section defined by the space between insulating barrier 65 and the boundary surfaces of notch 66. It is noted that in FIGS. 2-10, insulating barrier 65 is not shown nor is an arc chute shown. These elements are not present in order that the elements shown in these Figures may be illustrated with a greater degree of clarity.

Under overload conditions where current exceeds the current required for thermal tripping overcenter spring operating mechanism 25 is operated through the action of trip bar 67 releasing latch 36 which in turn releases latch tip 34 of cradle 32. Rod 67 is pivotally mounted at 68, and is biased in a clockwise direction by tension spring 69. The right end of rod 67, with respect to FIG. 2, extends into trip unit 35 for releasing latch 36, and the left end of rod 67 extends into the space between adjustable collars 71, 72 mounted on trip rod 70. The latter extends upward from magnet armature 73 which constitutes the movable part of the magnetic frame also including stationary yoke 74.

Spring 69 acting through rod 67 in engagement with collar 71 biases rod 70 upward.

Springs 76, extending between outboard pins 76a of auxiliary arm 39 and pin 76b extending through the bifurcated sections of main arm 38, have a line of action shiftable to opposite sides of pin 40. When the line of action of pin 40 is below pin 40 (FIG. 2) auxiliary arm 39 is biased counterclockwise and springs 76 provide contact pressure. Counterclockwise movement is limited by inwardly extending ears 380 which engage the right end of auxiliary arm 39. When the line of action of springs 76 is moved above pin 40 (FIG. 12) arm 39 is biased clockwise with this movement being limited by housing protrusion 77.

Under normal current conditions the current through coil 48 does not generate sufiicient flux to move armature 73 against the upward force exerted by spring 69. When current through circuit breaker 20 is in the range indicated by the first tripping step in FIG. 1, armature 73 is attracted to yoke 74 with a force sufiicient to move rod 70 downward so that collar 71 moves the left end of trip rod 67 downward, pivoting the latter counterclockwise and releasing latch 36 so that the energy stored in main spring 26 is effective to pivot contact arm 38, 39 thereby separating contact bridge 32 from stationary contacts 45, 46 (FIG. 3).

In the range of currents indicated by the second tripping step in FIG. 1, during the delay in operation of mechanism 25 lower collar 72 engages the right end of auxiliary arm 39 and physically pivots the latter about pin 40 with respect to main arm 38. This relative motion between main and auxiliary arms 38, 39 is increased as mechanism 25 moves main arm 38 in its opening stroke, and in so doing moves pin 40 upward with respect to FIG. 4 relative to roller collar 72. Thus, in the second tripping step, contact opening is achieved through the complementary action of both mechanism 25 and the physical force exerted by magnet 73, 74.

In the third tripping step of FIG. 1 the force exerted by magnet 73, 74 is so great that the speed of movement of rod 70 causes collar 72 in engagement with auxiliary arm 39 to move contact bridge 32 to full contact separation position before spring operated mechanism 25 has had time to move main arm 38 a substantial distance if at all (See FIG. 5).

In the fourth tripping step illustrated in FIG. 1, the conditions prevailing in the third tripping step (See FIG. 5) are exaggerated to the point where before main arm 38 is moved by mechanism 25 the engagement of collar 72 with auxiliary arm 39 begins to separate contact bridge 42 from stationary contacts 45, 46. However, before complete separation takes place due to the mechanical action of magnet 73, 74, the electrodynamic force described in detail in connection with FIGS. 8-11 come into play to assist in opening the contacts. Thus, in the fourth tripping step the'mechanical force exerted by magnet 73, 74 is complemented by the electrodynamic force acting between conductor 47 and bridging contact 42 to bring about rapid separation of the circuit breaker contacts.

In the fifth tripping step of FIG. 1, the current magnitude is so high that even before spring mechanism 25 of magnets 73, 74 is effective to cause contact separation, bridging contact 32 is moved to its fully opened position of FIG. 12 through the action of the electrodynamic force acting between bridging contact connecting section 55 and conductor section 470. This electrodynamic force pivots auxiliary arm '39 clockwise against the force of springs 76 thereby moving pins 76a upward and shifting the line of action for springs 76. When this line of action moves above pin 40, or overcenter, springs 76 aid the electrodynamic force to separate contacts 45, 46, 55, 56.

As seen in FIGS. 14-16, armature 73 is constructed in a manner to reduce the weight thereof, thereby permitting increased speed of operation. That is, the groups of arrowed generally circular lines 91, 92 illustrate the loop paths for flux when magnet 73, 74 is energized. Since the shaded area 73a of armature 73 is not included in either flux path 81 or 82 through stationary generally E-shaped yoke 74, the upper surface of annature 73 is cut away to provide a V-shaped notch in the shaded area 73a, thereby substantially reducing the weight of the iron laminations forming armature 73. These laminations are riveted to flared out portion 81 at the lower end of rod 70. Means (not shown) external to magnetic frame 73, 74 engage armature 73 to guide movement thereof toward and away from short center leg 84 of yoke 73.

Thus, it is seen that the instant invention provides a novel construction for a molded case current limiting circuit breaker, in which more rapid tripping action is obtained in the medium fault current range by utilizing mechanical forces of the tripping electromagnet to physical move the movable contact. The characteristic tripping curve for the breaker constructed in accordance with this invention is relatively smooth in that in various fault current ranges there is complementary action between the opening forces exerted by the spring operating mechanism, the tripping electromagnet, and the electrodynamic forces generated by currents flowing in opposite directions in adjacent conductors.

Although there have been described preferred embodiments of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows.

1. A circuit interrupter including first and second stationary contacts and a bridging contact means operable to electrically connect said contacts; said bridging contact means including a connecting section and first and second arms at opposite ends of said connecting section; said first and said second arms having respective first and second contact portions at one end thereof engageable with the first and second stationary contacts, respectively; a first conductor connected to said first contact and extending away from said bridging contact means; a second conductor connected to said second contact and ineluding a rigidly held section extending generally parallel to said connecting section in close proximity thereto; said sections arranged so that currents flow therethrough in opposite directions thereby generating magnetic fields which interact and generate a force acting between said sections to separate said bridging contact means from said stationary contacts.

' 2. A circuit interrupter as set forth in claim 1 in which the arms are generally L-shaped.

3. A circuit interrupter as set forth in claim 1 in which the stationary contacts project forward of the front surfaces of said conductors and rear surfaces of the contact portions engage forward surfaces of the stationary contacts; said contact portions projecting rearward of the portions of said arms in the vicinity of said contact portions.

4. A circuit interrupter as set forth in claim 3 in which the connecting section is rearward of said contact portions and the rigidly held section of the second conductor is rearward of said connecting section.

5. A circuit interrupter as set forth in claim 4 also including arm means; said bridging contact means mounted to said arm means at one end thereof; pivot means at the other end of said arm means and about which the latter is pivoted to operate said contact portions into and out of engagement with said stationary contacts.

6. A circuit interrupter as set forth in claim" 5 in which the arms extend from said connecting section in a direction away from said pivot means.

7. A circuit interrupter as set forth in claim 1 also including arm means; saidbridging contact means mounted to said arm means at one end thereof; pivot means at the other end of said arm means and about which the latter is pivoted to operate said contact portions into and out of engagement with said stationary contacts; said arms extending from said connecting section in a direction away from said pivot means.

8. A circuit interrupter as set forth in claim 7 in which the arms are generally L-shaped.

9. A circuit interrupter as set forth in claim 8 in which said arms are generally parallel to the plane in which said arm means is pivoted.

10. A circuit interrupter as set forth in claim 9 in which the stationary contacts are positioned on opposite sides of the plane in which the arm means in pivoted; said connecting section extending through said plane at right angles thereto.

11. A circuit interrupter as set forth in claim 1 in which the arm means at said one end thereof comprises an insulating means having a notch; an insulating barrier positioned between said stationary contacts in the plane of movement of said arm means and extending into said notch whereby said insulating means and said barrier cooperate to provide a relatively long are over the distance between said stationary contacts. 

1. A circuit interrupter including first and second stationary contacts and a bridging contact means operable to electrically connect said contacts; said bridging contact means including a connecting section and first and second arms at opposite ends of said connecting section; said first and said second arms having respective first and second contact portions at one end thereof engageable with the first and second stationary contacts, respectively; a first conductor connected to said first contact and extending away from said bridging contact means; a second conductor connected to said second contact and including a rigidly held section extending generally parallel to said connecting section in close proximity thereto; said sections arranged so that currents flow therethrough in opposite directions thereby generating magnetic fields which interact and generate a force acting between said sections to separate said bridging contact means from said stationary contacts.
 2. A circuit interrupter as set forth in claim 1 in which the arms are generally L-shaped.
 3. A circuit interrupter as set forth in claim 1 in which the stationary contacts project forward of the front surfaces of said conductors and rear surfaces of the contact portions engage forward surfaces of the stationary contacts; said contact portions projecting rearward of the portions of said arms in the vicinity of said contact portions.
 4. A circuit interrupter as set forth in claim 3 in which the connecting section is rearward of said contact portions and the rigidly held section of the second conductor is rearward of said connecting section.
 5. A circuit interrupter as set forth in claim 4 also including arm means; said bridging contact means mounted to said arm means at one end thereof; pivot means at the other end of said arm means and about which the latter is pivoted to operate said contact portions into and out of engagement with said stationary contacts.
 6. A circuit interrupter as set forth in claim 5 in which the arms extend from said connecting section in a direction away from said pivot means.
 7. A circuit interrupter as set forth in claim 1 also including arm means; said bridging contact means mounted to said arm means at one end thereof; pivot means at the other end of said arm means and about which the latter is pivoteD to operate said contact portions into and out of engagement with said stationary contacts; said arms extending from said connecting section in a direction away from said pivot means.
 8. A circuit interrupter as set forth in claim 7 in which the arms are generally L-shaped.
 9. A circuit interrupter as set forth in claim 8 in which said arms are generally parallel to the plane in which said arm means is pivoted.
 10. A circuit interrupter as set forth in claim 9 in which the stationary contacts are positioned on opposite sides of the plane in which the arm means in pivoted; said connecting section extending through said plane at right angles thereto.
 11. A circuit interrupter as set forth in claim 1 in which the arm means at said one end thereof comprises an insulating means having a notch; an insulating barrier positioned between said stationary contacts in the plane of movement of said arm means and extending into said notch whereby said insulating means and said barrier cooperate to provide a relatively long arc over the distance between said stationary contacts. 